1. Field of the Invention
The present invention relates to an electropneumatic converter comprising a displacement pump driven by at least one electric motor.
Such a converter is used, for example, in the biomedical field for the pneumatic control of a cardiac module, or artificial heart.
An artificial heart is formed mainly of two ventricle, each comprising a flexible bag or blood bag whose deformation for aspirating or delivering the blood is controlled by the deformation of a gas bag, for example an air or nitrogen bag. Each of the two gas bags, corresponding to each of the two ventricles, is connected periodically through a distributor to the inlet and to the outlet of the pump of an electropneumatic converter of the above type.
Such converters are already known, whose volume is however never less than 10 cubic decimeters or so, which makes it impossible to implant them in a patient. Serious disadvantages occur for the patient in whom a cardiac module has been implanted.
2. Description of the Prior Art
To overcome these drawbacks, a displacement pump is sought which, for a given delivery rate, has reduced volume. A pump is known offering this advantage, described in the British patent application published under the No. 2 123 089. It is a gear displacement pump with two gear wheels each of which is driven by its own electric motor, in which two independent electronic circuits are provided for controlling the motors, connected to computing means adapted for controlling the motors so that the teeth of the first toothed wheel are always in contact with the teeth of the second toothed wheel.
In this known pump, the reduction of volume, for a given delivery rate, is obtained because, since none of the toothed wheels is subjected to a drive torque by the other toothed wheel, as in a gear pump with a single motor, they may be dimensioned for withstanding only the load due to the pressure difference of the pumped fluid, which results in a reduction of the size of the toothed wheels.
The result is that if such a pump is used in a converter for the pneumatic control of an artificial heart, any breakdown occurring in one of the motors, or in one of the electronic circuits controlling the motors, is fatal for the converter since, as soon as a toothed wheel ceases to be driven by its own motor, it is subjected to mechanical stresses for which it has not been provided.
The present invention aims at overcoming this drawback.